During the coking process, an uneven heating of the oven door takes place. This will cause the oven door to warp. The extent of such warp increases with increasing oven height and door length. The warping effect has been dealt with by designing doors of extra hevy construction, but the increase of the material used causes increasing deformation because of rising diferentials in the temperature gradients. A lifting of the doors can couteract the closing pressure for each oven door and its two locking units. These locking devices act on the top and bottom third of the door against the coke oven door and press against the door with a force of up to 15 Mp against the door frame. As experience in oven operation has shown, even a perfect sealing strip does not prevent leakage, which causes considerable wear at the door frame, as the pressure is conducted in a linear direction over the sealing strip edges, which in turn causes depressions in the door frame.
The door stopper is made from high-heat resistant material, which protrudes into the oven chamber and which is connected to the door member and which keeps the oven filling at a distance from the door member. The stopper, together with the coke oven door, fulfills a multiple function. It is supposed to hold back the charge during the coking operation, minimize the heat load on the door member and ensure that the gas exhaust is led to a central gas collector at modern coke ovens. The door member forms a support bearing for the stopper and also closes the opening to the door frame to assure a tight seal. For sealing between door and frame, additional seals are provided, the most common form being a spring mounted bar design, which is supported by the door member and which pushes against the door frame by means of a knife edge when the oven doors are closed. Rough handling of the oven leads nevertheless to damage of the sealing edges. At the damaged spots, coking gas will escape during operation. Such leaks are undesirable because of their impact on the environment and the problems for the operators. For this reason, a number of tests have lately been conducted, to solve the problem of leakage. Conventional solutions have nevertheless remained unsatisfactory.